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The first thing I did was to constrain the map to black-and-white only so I could get clean selections. Image > Adjustments > Levels (Ctrl-L), and pull the handles on the histogram inward so that the grayscale information is removed.

Now I change the Mode to RGB so I can work with color later on: Image > Mode > RGB Color. If you already have more than one layer at this point, make sure you click "Don't Merge" in the dialogue box that pops up.

Select a country you want to add color to. I'm going to use England for this demonstration. For convenience in trying several techniques, I'll first save the selection: Select > Save Selection... and give it the name "England." The selection will now appear in the channels palette so I can reload it any time I want.

I'm also going to copy England into a new layer so I can experiment with that, too. Layer > New > Layer via Copy (Ctrl-J).

I name my original map layer "Europe" and the new layer "England" so I can keep track of what I'm doing.

The simplest way to accomplish the goal is to apply an Inner Glow layer style to the England layer. Select the layer, and click on the Layer Styles button. Choose "Inner Glow..."

In the dialogue box that follows, make sure "Preview" is checked and start playing with the options until you see something you like. Here are my settings:

At this point, it's probably a good idea to set a border stroke. Click the layer styles button and choose "Stroke..." I'm using a 1pt black stroke on each country.

Continue that process for all of the countries you want to appear on your map, making sure that no two adjacent countries have the same border color.

The easiest way to do this fast is to make all your layers, right-click on England, and choose "Copy Layer Style." Then select all your other layers (click on the top one and then shift-click on the bottom to select all of them), right-click on the selected layers, and choose "Paste Layer Style." All of the countries will receive the same inner glow and black stroke.

Now you simply need to go in and adjust the effect for each layer individually by double-clicking on the "Inner Glow" effect.

About 30 minutes later, I have this:

I've obviously been a bit sloppy. A bit more time spent in selections, and a better source image, would make this look a lot nicer. Now, I want to put this onto a nice parchment, so I go looking for a texture:

I place the texture behind all my country layers, and change the blending mode of each one to darken, so the white vanishes, leaving only the stroke and colored border behind.

Last edited by Midgardsormr; 01-29-2009 at 01:59 PM.
Reason: forgot the last image.

To get the interior of the country to be transparent, I used the blending mode. Each blending mode uses different rules for what it makes transparent. In this case, I used "darken," which causes any pixels in the selected layer that are lighter than pixels underneath it to become transparent. Since white is lighter than everything, all the white will vanish when the layer is set to darken.

Conversely, if you fill the country with black and set it to "lighten," you'll get the same result--lighten turns pixels transparent if they're darker than what's underneath.

Might I suggest perhaps fading the inner glow farther in and filling the countries with a slightly off white version of their glow color.

Thanks for the rep.

Good idea. If this were a serious map, I'd adjust the size of the glow for each country. It's just about perfect for Denmark, but way too small for France. The fill I could take or leave, depending on how I felt; I've done it both ways, though this is the first time I've used Photoshop for this style.